The Effect of Sample Site, Illness Duration, and the Presence of Pneumonia on the Detection of SARS-CoV-2 by Real-time Reverse Transcription PCR

Stephanie Sutjipto; Pei Hua Lee; Jun Yang Tay; Shehara M Mendis; Mohammad Yazid Abdad; Kalisvar Marimuthu; Oon Tek Ng; Lin Cui; Monica Chan; Margaret Soon; Raymond T P Lin; Yee-Sin Leo; Partha P De; Timothy Barkham; Shawn Vasoo; National Centre for Infectious Diseases COVID-19 Outbreak Research Team

doi:10.1093/ofid/ofaa335

The Effect of Sample Site, Illness Duration, and the Presence of Pneumonia on the Detection of SARS-CoV-2 by Real-time Reverse Transcription PCR

Open Forum Infect Dis. 2020 Aug 3;7(9):ofaa335. doi: 10.1093/ofid/ofaa335. eCollection 2020 Sep.

Authors

Stephanie Sutjipto^{1

2}, Pei Hua Lee^{1

2}, Jun Yang Tay^{1

2}, Shehara M Mendis³, Mohammad Yazid Abdad⁴, Kalisvar Marimuthu^{1

2

5}, Oon Tek Ng^{1

2

6

5}, Lin Cui⁷, Monica Chan^{1

2

6

5}, Margaret Soon², Raymond T P Lin^{7

5}, Yee-Sin Leo^{1

2

6

5

8}, Partha P De³, Timothy Barkham^{3

5}, Shawn Vasoo^{1

2

4

6

5}; National Centre for Infectious Diseases COVID-19 Outbreak Research Team

Collaborators

National Centre for Infectious Diseases COVID-19 Outbreak Research Team:
Sean Wei Xiang Ong, Brenda Sze Peng Ang, David Chien Lye, Poh Lian Lim, Cheng Chuan Lee, Li Min Ling, Lawrence Lee, Barnaby Edward Young, Tau Hong Lee, Chen Seong Wong, Sapna Sadarangani, Ray Lin, Deborah Hee Ling Ng, Mucheli Sadasiv, Po Ying Chia, Chiaw Yee Choy, Glorijoy Shi En Tan, Frederico Dimatatac, Isais Florante Santos, Chi Jong Go, Yeo Tsin Wen, Yu Kit Chan, Pooja Rao, Jonathan W Z Chia, Constance Yuan Yi Chen, Boon Kiat Toh

Affiliations

¹ Department of Infectious Diseases, Tan Tock Seng Hospital, Singapore.
² National Centre for Infectious Diseases, Singapore.
³ Department of Laboratory Medicine, Tan Tock Seng Hospital, Singapore.
⁴ Infectious Disease Research Laboratory, National Centre for Infectious Diseases, Singapore.
⁵ Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
⁶ Lee Kong Chian School of Medicine, Singapore.
⁷ National Public Health Laboratory, National Centre for Infectious Diseases, Singapore.
⁸ Saw Swee Hock School of Public Health, National Centre for Infectious Diseases, Singapore.

Abstract

Background: The performance of real-time reverse transcription polymerase chain reaction (rRT-PCR) for SARS-CoV-2 varies with sampling site(s), illness stage, and infection site.

Methods: Unilateral nasopharyngeal, nasal midturbinate, throat swabs, and saliva were simultaneously sampled for SARS-CoV-2 rRT-PCR from suspected or confirmed cases of COVID-19. True positives were defined as patients with at least 1 SARS-CoV-2 detected by rRT-PCR from any site on the evaluation day or at any time point thereafter, until discharge. Diagnostic performance was assessed and extrapolated for site combinations.

Results: We evaluated 105 patients; 73 had active SARS-CoV-2 infection. Overall, nasopharyngeal specimens had the highest clinical sensitivity at 85%, followed by throat, 80%, midturbinate, 62%, and saliva, 38%-52%. Clinical sensitivity for nasopharyngeal, throat, midturbinate, and saliva was 95%, 88%, 72%, and 44%-56%, respectively, if taken ≤7 days from onset of illness, and 70%, 67%, 47%, 28%-44% if >7 days of illness. Comparing patients with upper respiratory tract infection (URTI) vs pneumonia, clinical sensitivity for nasopharyngeal, throat, midturbinate, and saliva was 92% vs 70%, 88% vs 61%, 70% vs 44%, 43%-54% vs 26%-45%, respectively. A combination of nasopharyngeal plus throat or midturbinate plus throat specimen afforded overall clinical sensitivities of 89%-92%; this rose to 96% for persons with URTI and 98% for persons ≤7 days from illness onset.

Conclusions: Nasopharyngeal specimens, followed by throat specimens, offer the highest clinical sensitivity for COVID-19 diagnosis in early illness. Clinical sensitivity improves and is similar when either midturbinate or nasopharyngeal specimens are combined with throat specimens. Upper respiratory specimens perform poorly if taken after the first week of illness or if there is pneumonia.

Keywords: SARS-CoV-2; illness duration; pneumonia; rRT-PCR; sample site.